What ‘Aha!’ really sounds like; the back story of detecting gravitational waves

A team at the Harvard-Smithsonian Center for Astrophysics announced Monday they found the first direct evidence of cosmic inflation. Top to bottom, Marc Kamionkowski of Johns Hopkins University, Clem Pryke of University of Minnisota, Jamie Bock of Caltech/JPL, Chao-Lin Kuo of Stanford/SLAC, John Kovac of Harvard-Smithsonian Center for Astrophysics.

At the press announcement at the Harvard-Smithsonian Center for Astrophysics, many of the questions focused on what this result meant for the future of physics and just how profound it was—not only giving insight into the birth of the universe 13.8 billion years ago, but also proving Einstein’s general theory of relativity, and even providing evidence of a phenomenon famed British cosmologist Stephen Hawking had predicted.

Max Tegmark, an MIT physicist, said that this result was one of the “grandest prizes in science,” and there are other teams that were scooped yesterday. But the prize is the end of a nerve-wracking, painstaking process. The real work isn’t seeing the great result, but still seeing that result after you’ve worked your hardest to prove yourself wrong. Only after all that do scientists dare declare that, Aha! Only after they’d tried every trick to show that they weren’t making a mistake would they really believe they had measured a swirly pattern of polarized light that is the clearest evidence yet of long-sought gravitational waves.

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The South Pole telescope, called BICEP2, that took these measurements, collected data from 2010 to 2012. Researchers then spent a long time analyzing the measurements.

At the press conference, I asked the panel when and how they each grasped that they might actually be detecting the signal they were seeking. It can be difficult for non-scientists to understand just what kind of work, excitement, and self-doubt goes into a discovery. It isn’t like the universe just lays down its hand and shows its cards because the right kind of telescope has been built; a delicate measurement like this one requires persistence and skepticism and months of work to make sure it isn’t an artifact.

In the current experiment, for example, key moments included comparing measurements with results from other telescopes. Those cross-checks were an essential ingredient in showing that they had something more than an aberration on their hands.

The scientists each had a slightly different answer to the question, “When did you know? And how did you know?” and I present their answers in mildly edited form, below. Here’s what “Aha!” really sounds like.

Clem Pryke, associate professor at the University of Minnesota: “Well, it’s been a tremendously exciting process. It’s been described at times in our group as an emotional roller coaster.”

“It’s mind-boggling to go looking for something like this and actually find it. ... The world of experimental physics is littered with guys who spent decades searching for something. It’s just been a really incredible experience to actually find what we’re looking for. Of course, we write grant proposals and make it look like we’re going to find it. It’s one thing to say that and another thing to really believe it in your heart.”

Jamie Bock, professor of physics at CalTech: “I distinctly remember our collaboration in the last year, where the first half of the meeting, we had been thinking, ‘We’ve got to get a paper out and let’s just try to set an upper limit.’ And the data wouldn’t cooperate. And then the second day, I think someone showed a cross-spectrum and then it just dawned on everyone: Well, maybe this really is real. And then we had this one-year odyssey of doing all the testing.”

Chao-Lin Kuo, assistant professor at Stanford University: “There is variation among the four of us and everybody in the collaboration, as well. Me, personally, I started to think maybe this is real about six months ago, 50-50 and that became 90 and 95, and so on.”

John Kovac, associate professor of astronomy at Harvard-Smithsonian Center for Astrophysics: “That’s part of the process and part of the strength of having so many of us scrutinize this with different kinds of skepticism. ... The story that we’re testing with this data set sounds so fantastical! We know it’s good physics, but the extrapolation from the physics that we understand, combined with these models that have been built by theorists, to testable predictions, come from such an exotic regime—the beginning of our universe.” “We needed a lot of convincing the signal was real. The emotional process for us was helped by setting a series of concrete tests and milestones passed through the end of last year. And by the end of December, it was passing each of these tests.”